1. Field of the Invention
The present invention relates generally to an apparatus for and method of stacking articles, and in particular to an apparatus for and method of stacking flexible articles of non-uniform thickness while maintaining the uppermost article in a substantially horizontal orientation.
2. Description of the Related Art
In the final stages of production of flexible articles such as, for example, plastic zipper or slider bags, an orbital packer or similar device delivers the bags to a delivery point where they are stacked in preparation for packaging. At the delivery point, the first few bags of a stack typically are received on retractable count fingers while the previous stack is being removed from a stacking table, which is itself typically comprised of a plurality of fingers. Thereafter, the count fingers pass through the stacking table, depositing the first few bags of the new stack on the stacking table. Once a predetermined quantity of bags has been stacked on the stacking table, typically twenty-five, the count fingers again are deployed to separate the stack just formed from the continuous stream of bags, allowing removal of the stack while the next several bags begin forming a new stack on the count fingers. The process then repeats for each subsequent stack. The stacks formed on the stacking table are removed by a horizontal transfer mechanism, such as that disclosed in U.S. Pat. No. 4,588,070.
It is difficult to efficiently and neatly stack articles such as plastic bags using commercial, high-speed stacking machinery. This is due to the flexibility of these articles and their slippery surfaces (which aid in extrusion and film formation processes). If the bags are of non-uniform thickness, as they often are, stacking is even more difficult. For example, zipper bags have mating zipper elements along just one edge of the bag. A typical stack of twenty-five plastic zipper bags may be 2.0 inches or more thick at the zippered end (twenty-five times the thickness of the opposing pair of zipper elements), while being only 0.10 to 0.20 inches thick at the opposite end (twenty-five times the two-ply bag film thickness). If sliders are employed on the zippered end, the thickness differential is even greater. In the stacking of such bags, the uppermost bags in a stack are frequently disturbed by subsequent bags being deposited onto the stack. The slope created by the non-uniform thickness of the bags, coupled with the impact of subsequent bags being stacked, typically causes the uppermost bags to slide down the stack toward the end opposite to the zipper, resulting in shingled, rather than stacked, bags.
U.S. Pat. No. 5,302,080, assigned to the same assignee as the present invention and incorporated herein by reference in its entirety, discloses a stacking apparatus designed to alleviate some of the above-noted problems. The apparatus includes means for supporting the bags which moves downward as bags are stacked thereon so that the uppermost bag in a stack is maintained at a substantially constant height. In one embodiment, the means for supporting the bags is tilted as subsequent bags are deposited on the stack, thus maintaining the uppermost bag in a substantially horizontal orientation. In another embodiment, first and second supporting means cooperate to accomplish this same result. The first supporting means, on which the non-zippered portions of the bags rest, is maintained in a generally horizontal orientation as it moves downward. The second supporting means, on which the zippered portions of the bags rest, moves downward relative to the first supporting means. In each embodiment, a pair of cams is commonly supported on and rotatable with a drive shaft to regulate the overall downward movement of the supporting means, as well as the tilting of the supporting means or the movement of the second supporting means relative to the first supporting means. While this apparatus has been useful in overcoming some of the above-noted problems with the stacking of flexible articles of non-uniform thickness, its construction is relatively complex. Moreover, because the cams that regulate movement of the supporting means are affixed to a drive shaft, the relative movement of one portion of the supporting means relative to another portion thereof cannot be adjusted without shutting down the apparatus and replacing one or more parts. Consequently, there is no way to make adjustments to the apparatus while it is operating. In addition, the apparatus is not readily adaptable for switching between bags having different thicknesses or bags employing different closure mechanisms, or for forming stacks consisting of a different number of bags.
Accordingly, there is a need in the art for a simplified apparatus for and method of stacking articles of non-uniform thickness in neat stacks by maintaining the uppermost article in a substantially horizontal orientation and at a substantially constant height.
There is a further need for such an apparatus and method wherein opposite ends of a stacking table can descend by different amounts, and the difference can be adjusted without having to replace any parts of the apparatus.
There is a still further need for such an apparatus and method wherein the difference in amount of descent of opposite ends of a stacking table can be adjusted even while the apparatus is operating.
The present invention addresses the foregoing needs in the art by providing an apparatus for and method of stacking articles, in which separate support surfaces descend by different amounts, and the difference is readily adjustable.
In a first aspect of the present invention, a stacking apparatus includes a stacking table for receiving a plurality of articles. The stacking table includes separately movable first and second portions. The apparatus further includes means for moving the stacking table through a range of motion, means for displacing the second portion of the stacking table relative to the first portion of the stacking table as the stacking table is moved through the range of motion, and means for adjusting a relative distance by which the displacing means displaces the second portion of the stacking table relative to the first portion of the stacking table.
In another aspect, a stacking apparatus includes a stacking table for receiving a plurality of articles. The stacking table includes separately movable first and second portions. The apparatus further includes means for moving the stacking table through a range of motion, and means for displacing the second portion of the stacking table relative to the first portion of the stacking table in response to movement of the stacking table through the range of motion by the moving means.
In yet another aspect, a stacking apparatus includes a stacking table having separately movable first and second support surfaces, a selectively stationary cam plate having a cam surface, and an actuator for moving the stacking table through a range of motion relative to the cam plate. A cam follower is mechanically coupled to the second support surface and located to engage the cam surface when the stacking table is moved go through at least part of the range of motion, so that when the actuator moves the stacking table and the cam follower engages the cam surface, the second support surface is displaced relative to the first support surface.
In still another aspect, a stacking method involves delivering a plurality of articles sequentially at a delivery height to a stacking table having a first support surface and a second support surface. The stacking table is lowered relative to the delivery height so that each subsequent article delivered to the stacking table is stacked on top of a previous article at substantially the delivery height. Simultaneously with this lowering step and responsive to the lowering of the stacking table, the second support surface is displaced downward relative to the first support surface.
In a further aspect, an apparatus for stacking sequentially a plurality of articles, each having a relatively thin portion and a relatively thick portion, includes a stacking table for receiving the plurality of articles. The stacking table has a first support surface for supporting the relatively thin portion of the articles and a second support surface for supporting the relatively thick portion of the articles. The apparatus further includes a cam plate having a cam surface, an actuator coupled to the stacking table for moving the stacking table through a range of motion relative to the cam plate, and a lever pivotally mounted relative to the stacking table and linked to the second support surface. A cam follower is connected to the lever so that as the stacking table is moved through at least part of the range of motion, the cam follower engages the cam surface, thereby pivoting the lever to displace the second support surface relative to the first support surface.
In a still further aspect, a stacking method involves delivering a continuous stream of articles sequentially to a stacking table at a delivery height. Each article has a relatively thin portion and a relatively thick portion. The stacking table to which the articles are delivered includes a first support surface for supporting the relatively thin portion of the articles and a second support surface for supporting the relatively thick portion of the articles. The second support surface is biased upward into horizontal alignment with the first support surface by a spring. The method further involves lowering the stacking table relative to the delivery height, so that each subsequent article is stacked on top of a previous article at substantially the delivery height, and downwardly displacing the second support surface a vertical distance relative to the first support surface against the upward biasing of the spring, such that the uppermost article in the stack is maintained in a substantially horizontal orientation.
In another aspect, a stacking apparatus includes a stacking table for receiving a plurality of flexible articles, each having a non-uniform thickness. The stacking table includes separately movable first and second support surfaces. The apparatus further includes a frame on which the first support surface is mounted, an elongated reciprocating member coupled to the second support surface, a spring for biasing the second support surface upward relative to the frame, and a lever having two arms disposed at an angle relative to one another. The lever is pivotally coupled to the frame near an intersection of the two arms of the lever, and has a cam follower mounted on one arm thereof. At the other arm, the lever is pivotally coupled to the reciprocating member. The apparatus also includes a selectively stationary cam plate having a cam surface for engagement with the cam follower, and an actuator coupled to the stacking table for moving the stacking table downward relative to the cam plate. As the actuator moves the stacking table downward, the cam follower engages the cam surface, causing the lever to pivot so as to displace the second support surface downward relative to the first support surface against the upward biasing of the spring.
A better understanding of these and other objects, features, and advantages of the present invention may be had by reference to the drawings and to the accompanying description, in which there are illustrated and described preferred embodiments of the invention.